The many advantages offered by laser surgery has made the technique very popular in surgical procedures spanning the different branches of medicine. Some estimates have indicated that as many as 1 million surgical procedures are performed each year which involve the use of lasers at some stage. Of this number, approximately half are performed endoscopically, and the remainder can be classified as "open" laser surgery. The latter category suffers from a much greater incidence and probability of inadvertent exposure to powerful and destructive laser light. Practically all the objects in the operating room, including medical equipment and personnel, are potential accidental targets of a direct or reflected beam.
The outcome of accidental exposure to both focused and unfocused laser light includes burns to human tissues, damage to equipment, ignition of combustible materials including ordinary fabrics and any flammable materials. The danger from fires started by unfocused laser light is particularly acute.
For example, a recent communication by Turut, P. et al. in Bull. Soc. Opht. France 1988, 5, LXXXVIII chronicles the results of mistakes made by careless operators of laser equipment: lens burns with argon laser, corneal burns in laser iridotomy, intraocular lens marks after YAG posterior capsulotomy, retinal burns with YAG laser, and other serious complications. Rather dramatic fires and even explosions have been reported in the combustion of endotracheal tubes upon exposure to CO.sub.2 laser light (See, for example, Sosis, M. B. in Anesth. Analg. 1989, 68, 392-3 in which the author reports the results of attempts to protect endotracheal tubes with metallic tape). Another article specifically referring to laser drape fires is by Bauman, N., "Laser Drape Fires: How Much of a Risk?", Laser Medicine & Surgery News and Advances, August 1989.
It is apparent that conventional surgical drapes made of cellulose or other combustible materials, including synthetic polymers, offer little protection and, in fact, constitute a fire hazard in an operating room in which lasers are in use. Frequently, the medical practitioner has even resorted to using towels soaked in saline in an effort to obtain better protection than a dry cloth drape. Besides being hygienically unsuitable, such towels have been known to dry out during the medical procedure and ignite upon accidental exposure to the laser. Other means of protection which purportedly shield healthy tissue or equipment from the harmful beams are known and have taken the form of barriers or laser drapes. A metallic blanket comprising a polymeric inner sheet completely enclosed by aluminum foil is described in U.S. Pat. No. 4,715,366 issued to Teeple. Cotton gauze, woven textile fabrics, and elastomeric materials such as a pliable polyolefin are recited as possible examples of inner sheets. It is specified that the inner sheets remain moldable or drapable while being resistant to melting or ignition. While such a metallic blanket may possibly be effective in preventing the immediate penetration of a laser beam (no experimental data are provided), such a metallic blanket most certainly lacks the ability to adequately and quickly disperse away from tissue the large concentration of heat generated at the vicinity of the incident beam. In addition, the possibility that the inner materials may ignite remains, or worse, areas of the sheet may become so hot as to burn the tissue sought to be protected underneath the metallic blanket. It is crucial to note that many patients would be under general anesthesia and would be unable to feel, much less communicate, any discomfort. Moreover, a reflective exterior surface such as that provided by an aluminum foil exterior, may exacerbate the danger arising from reflected or deflected beams.
Another means for protecting healthy tissue from stray laser light which utilizes a conventional hydrogel as the surgical drape material, is disclosed in U.S. Pat. No. 4,601,286 issued to Kaufman. A specific embodiment recited in this reference includes a metallic sheet interposed between two layers of hydrogel material. It is apparent from the disclosures of this reference that any protection accorded by these laser shields applies only to a CO.sub.2 laser operated at low power (15 watts), if that. Although one might expect an embodiment having a metallic sheet interposed between two layers of hydrogel to perform better than layers of plain hydrogel, such expectation does not necessarily hold. It has been found, in fact, that the metallic sheet, such as an aluminum foil, which is present within the hydrogel bursts outward towards the source of the laser light, presumably, because of the pressure exerted by the gases building up underneath the metallic sheet upon extended exposure of the shield to a focused stationary beam. Having suffered a loss in its integrity, the metallic sheet is no longer able to provide any protection. Furthermore, the behavior of these laser shields when the CO.sub.2 laser is operated at higher intensity or when shorter wavelength (higher energy) lasers are used is quite suspect. Moreover, the bare sheet of aluminum foil tends to become crinkled or torn, especially during processing, separating from the hydrogel sheet and eventually corroding from the effects of air and moisture. Indeed, these prior art materials have very poor shelf lives with the metal rapidly corroding and initiating the degradation of the hydrogel itself. Corroded materials are, of course, unsuitable for use in any hospital environment.
Of equal significance, the reflective nature of the facing surface produces a glare under the high intensity lamps of an operating room making it difficult for surgeons and nurses to operate. Other deficiencies of these laser shields include their failure to alleviate the concern for stray laser light reflected off of the shiny metallic surface of the bare foil. The possibility that water or other aqueous solutions may need to be added to the laser shield dressing, especially where wet towels are also used, to replace water lost during the surgical procedure, also adds yet another item to be considered and monitored by the already highly stressed and burdened surgical team. Lastly, this reference fails to recognize, much less address, the danger associated with the ignition of combustible materials due to direct exposure to focused or unfocused laser light.
A laser-resistant back-up pad is described in U.S. Pat. No. 4,520,814. This pad which is meant to be inserted between layers of incised tissues and is comprised of an elastomeric, rubber substrate over which is bonded a coating of a mixture of elastomer and a metal powder. A wet gauze is preferably placed over the resulting pad. The laser reflective coating described is initially a solution which is applied separately and needs to be dried and/or cured, preferably baked.
Thus, a need for a protective drape which is conformable, capable of withstanding incident laser light of varying wavelengths at high power settings, capable of adequately dispersing the heat generated by the incident beam, which is easily processable, and one which has stable long-term storage characteristics remains unfulfilled. Furthermore, such a protective drape must eliminate or greatly reduce the possibility of stray laser light reflecting off of the protective drape and inadvertently causing harm or injury to adjacent objects or tissue. Most importantly, such a drape must provide adequate protection for a significant length of time without suffering catastrophic failure such as the bursting phenomenon observed with existing laser drapes. Additionally, the outward facing surface of an ideal drape should be substantially non-reflective. It is also most desirable that a protective drape be found which has all the characteristics enumerated above and also be readily sterilizable for use in an asceptic environment and, furthermore, have the versatility to accommodate various additives.